Plasmids are circular pieces of DNA that exist in the cytoplasm of many bacteria independent of the chromosome. They vary in size and number among bacterial strains and are conserved generally in each of the daughter cells after replication. Detection of plasmids in a bacterial isolate can provide a unique "fingerprint" for that strain and may provide a powerful epidemiologic tool in studying the identity (clonality) of strains isolated from different sources or patients. Traditional techniques for isolating plasmids require large volumes of cells, sophisticated equipment, and days of preparation. We are adapting these methods so that plasmids can be isolated from small volumes using equipment commonly available in the clinical laboratory. Also, the methods should be simple and rapid enough to allow large scale screens of isolates. These methods will be available then for epidemiologic studies. We have developed three step methods for the isolation of plasmids from staphylococcal and Gram negative bacillary isolates. The methods have given consistently, reproducible results and have been used to identify clonality in campylobacter and staphylococcal isolates.